Damage to the basal layer of the endometrium may be detected by ultrasound, but it is not as accurate as hysteroscopy. If uneven echoes of the basal layer are seen on ultrasound, calcification and liquefaction are present, and the endometrium is too thin. In this case a hysteroscopy is needed to further examine the extent of damage to the endometrial basal layer. Most of the endometrial basal layer damage is caused by multiple uterine operations, such as endometrial damage caused by abortion, submucosal myomectomy, endometrial electrosurgery, and so on. A vaginal ultrasound examination reveals uneven echogenicity of the basal layer, and the endometrium is found to be thin before the onset of menstruation. In this case, a hysteroscopy is recommended, which allows direct visualization of the severity of endometrial damage.